This invention relates to a plasma surface treatment method and apparatus for treating a film surface by using plasma with a high efficiency.
There are known techniques for reforming the surface of a substrate made of various materials by making gas in a plasma state act on the surface. For example, for polymers, as discussed in an article entitled "Plasma niyoru Kobunshi Zairyo no Hyomen Shori (Surface Treatment of polymer materials by using plasma)" (Kogyo Zairyo (Industrial Materials), Vol. 32, p.24-30 (1982)), various kinds of applications are conceived, such as techniques, by which hydrophilic radicals are introduced in the surface by making oxygen plasma act thereon in order to improve the adhesivity of paints, plasma etching techniques using ion energy and reactions of active radicals, etc.
If it were possible to effect continuously such a plasma surface treatment on a long film, productivity thereof would be considerably increased. For this reason a continuous plasma surface treating apparatus has been proposed, as disclosed e.g. in JP-A-57-18737.
Also, as known apparatuses similar thereto, there are known continuous plasma surface treating devices disclosed in JP-A-59-91128 and JP-A-59-91130. In these kinds of apparatuses film is rolled on a rotating cylindrical treating drum disposed in a vacuum chamber and continuous plasma surface treatment for the film is effected by supplying electric power to a counter electrode disposed adjacent the side surface of the treating drum to produce plasma, while forwarding the film in one direction in synchronism with the rotation of the treating drum.
In this case, in order to increase the efficiency of the plasma surface treatment, conditions of the atmosphere for projecting high energy ions to the film are necessary. However, according to the prior art techniques described above, the treating drum is grounded and the potential difference between the treated surface and the plasma is at most only several tens of volts, even if a high frequency voltage of 13.56 MHz, which is a commercial frequency, is applied to the counter electrode to produce plasma. If the treating drum is not grounded and a negative high voltage is applied thereto, positive ions in the plasma are accelerated and in this way it is possible to increase the efficiency of the plasma surface treatment by using this energy. However, in the case where a high voltage is applied to the rotating treating drum, it gives rise to problems that (1) the mechanism becomes complicated, because a high voltage is applied to a rotating body, that (2) there is a fear that unnecessary discharge is produced, because parts other than the treated portion of the rotating drum are raised to the high voltage and that ( 3) when a metal film is disposed on the film, the metal film itself should be raised to the high voltage, and for this reason the feeding and rewinding mechanism is also raised to the high voltage, which complicates the insulating scheme therefor.